Disentangling associations between pubertal development, healthy activity behaviors, and sex in adolescent social networks

With the onset of puberty, youth begin to choose their social environments and develop health-promoting habits, making it a vital period to study social and biological factors contextually. An important question is how pubertal development and behaviors such as physical activity and sleep may be differentially linked with youths’ friendships. Cross-sectional statistical network models that account for interpersonal dependence were used to estimate associations between three measures of pubertal development and youth friendships at two large US schools drawn from the National Longitudinal Study of Adolescent to Adult Health. Whole-network models suggest that friendships are more likely between youth with similar levels of pubertal development, physical activity, and sleep. Sex-stratified models suggest that girls’ friendships are more likely given a similar age at menarche. Attention to similar pubertal timing within friendship groups may offer inclusive opportunities for tailored developmental puberty education in ways that reduce stigma and improve health behaviors.

3. We note that you have indicated that there are restrictions to data sharing for this study.PLOS only allows data to be available upon request if there are legal or ethical restrictions on sharing data publicly.For more information on unacceptable data access restrictions, please see http://journals.plos.org/plosone/s/data-availability#locunacceptable-data-access-restrictions.Before we proceed with your manuscript, please address the following prompts: a) If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially identifying or sensitive patient information, data are owned by a third-party organization, etc.) and who has imposed them (e.g., a Research Ethics Committee or Institutional Review Board, etc.).Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent.Authors: We have expanded our "data availability" statement to read as follows: This research uses third party data from the National Longitudinal Study of Adolescent to Adult Health (Add Health).Information on how to obtain the Add Health data files is available on the Add Health website (http://www.cpc.unc.edu/addhealth).To apply for these data, the researcher must request access and download a contract application from the UNC Carolina Population Center Data Portal (https://data.cpc.unc.edu/projects/2/view).Once completed, researchers must submit their application through the portal.Data used in the current study were not collected by the study authors and therefore we do not have the permission to share the data.The data used are restricted use data from the Add Health study.Researchers who wish to gain access to this data must apply for access using the information specified above.The authors did not have any special access privileges to the data and confirm that the data was obtained in the same manner outlined above.Relevant codes for replicating analyses are within the Supporting Information files of this manuscript.
In crafting this availability statement, we followed guidance of recent scholars who have recently published in PLOS ONE using these restricted data as well  We thank the reviewers for their helpful suggestions.In what follows, we respond point-by-point to reviewer concerns, with text additions underlined and italicized.We add numbers to each critique if reviewers did not include numbers, indicated with [#].
Reviewer #1: This article presents a scientific approach to identifying key factors establishing friendships in pubertal age group adolescents.Network analysis posits an interesting approach to analyze this sociological phenomenon.
The authors summarize a vast evidence base of literature on physical activity and sleep which lays good groundwork for the study.My review points are: 1.In the first line of the introduction, the authors may want to change the word "outsize".Authors: We appreciate R1's introductory comments praising our approach (network analysis) and synthetic overview of relational health behavior research on physical activity and sleep.We have changed the word "outsize" to "disproportionate".

Specifically, for both boys and girls, later adolescent physical development was prospectively associated with reporting more sleep nightly as young adults."
3. The authors may want to expand on network analysis basics for the naive reader.
Authors: This is a welcome suggestion; indeed, on reflection, our analytic approach section launched into a highly technical form of social network analysis before giving a more general introduction.With space limitations in mind, we direct readers to useful guides and have revised this section (p15) to now read:

"Social network analysis (SNA) is a field of inquiry that seeks to explain the causes and consequences of patterned social relationships among humans; a wealth of useful guides are readily accessible [e.g. 62, 63, 64]. A key feature of SNA is a practical and statistical concern not just for individual attributes and qualities, but also a concern with quantities and qualities of ties between individuals and how -together -individuals and their social ties are connected with a given phenomenon. One type of SNA, exponential random graph models (ERGMs), were used to test study hypotheses and estimate determinants..."
4. The study draws on data from the 1994-1995 study, a timeline when millenials were in the puberty.Given that we are in a different generation now, the authors may want to add this as a limitation for the generalizability of the study.Also, the use of devices have changed over time.Authors may wat to comment on this.

Authors: We appreciate the reviewer's concern about generational differences between now and youth at the time of data collection, and we have further expanded upon our statements about these generational differences (p14) to have a revised subheader: "Considerations regarding modern adolescent socialization, pubertal development, and activities." In this section we now note: "In terms of pubertal development, the onset of puberty has rapidly declined since the industrial revolution [59] and has continued to decline (albeit more slowly) during the past several decades [60, 61]." • We agree that the use of devices have changed over time, and we expand upon our prior statement (p14) that, "It is important to note that how adolescents socialize in today's smartphone era differs considerably from the 1990s…" and append the statement that "Screens are now ubiquitous in a way that is qualitatively different from youth experiences with visual media in the 1990s."
5. The assessment of pubertal development seems to be limited due to the tool used and the authors may want to allude to this as well.
Authors: We have expanded upon our prior statement in the limitations section of the discussion to be more explicit about this point.If these recommendations are addressed, this paper may be suitable for publication but otherwise the paper possibly only has limited historical value and hence should be rejected.Authors: We appreciate the close read and the 7 recommendations that Reviewer 1 has offered.To make our philosophical position clearer for readers, we have expanded upon our commentary regarding modern youth socialization (p14) to now explicitly state that, "…we take the position that these analyses can be informative to the current era and not simply historical analysis, a point we return to in our conclusions."In the conclusions section (p26-27) we expand upon this point considerably.
Reviewer #2: The paper attempts to explore an interesting area of research regarding the interactions between pubertal development, healthy activity behaviors, and social networks among adolescents.A few points to improve the article.
[1] The paper's extract lacks comprehensiveness by omitting the study's findings and conclusions.It focuses primarily on the abstract, introduction, and methods, which leaves a reader without a full understanding of the research's outcomes.There should be a different heading of Conclusions Authors: Thank you for this comment.We will admit to being slightly confused by Reviewer 2's phrase "The paper's extract lacks comprehensiveness…" and would appreciate further guidance.If the reviewer meant "abstract", we have re-examined the abstract and do think that it offers a capsule summary of statement of our scientific problem, how and why we go about studying this problem, a brief statement of findings, and brief comment about implications.If this comment is related to the discussion, we also want to clarify that we have now added a new heading for "Conclusions and Practical Applications"" (related to R2, comment 4) to further expand on the study's findings and conclusions" [2] Discuss the limitations of cross-sectional data in establishing cause-effect relationships.It is mentioned in one line only.
Authors: We appreciate that there are a variety of ways that cross-sectional data can limit our understanding of cause-effect relationships.We have revised our former statement (p24

as follows: "A perennial observational research concern is reciprocal causation (i.e. whether friendship changes cause behavioral shifts, or whether behaviors lead to friendship). Without more granular longitudinal information on behavior and friendship changes to establish temporal ordering, a cross-section of yearly data can provide insight into associations, but cannot provide causally informative evidence of statistical relationships."
[3] The absence of a discussion on the generalizability of findings diminishes the argument's broader relevance, especially when data is drawn from specific settings.Comment on this in the limitation as well.
Authors: We appreciate this concern, and we agree.We take the position that it is a strength to treat each school as having its own 'network ecology', following the work of McFarland and colleagues -and we do not make claims to generalizability to all schools.We have now appended a statement on p25 to, "Yet it would be inappropriate to claim that our findings generalize to all schools.Given differences in school types, sizes, student composition, and cultures, care and thoughtfulness are warranted in applying these findings to school settings beyond the two types studied here.

As McFarland and colleagues [43] point out in relational analyses of multiple school environments, giving attention to specific network ecologies of different schools is critical in considering how interventions might be implemented most successfully. Our study follows suit, demonstrating that it is important for the study of pubertal development to account for the network context of other physical health-promoting behaviors (PA, sleep) and risk factors (ST, weight status) that may independently shape, as well as confound, puberty's relationship with friendship formation."
[4] Discuss the practical implications and real-world applications as a separate heading to enhance its relevance beyond academic circles.Authors: Thank you for this comment; we have endeavored to address this concern in tandem with the first comment.
Reviewer #3: Thank you for the opportunity to review the manuscript, "Disentangling associations between pubertal development, healthy activity behaviors, and sex in adolescent social networks."The study is a detailed analysis of how pubertal timing/development, physical health, sleep, and biological sex influence friendship formation in adolescents.The paper is very well-written and provides sufficient detail on the study, methods, and findings.Overall, this is an interesting paper that contributes to the literature by using a novel statistical approach to the question of whether puberty, physical health, and more influence friendship formation.With these strengths in mind, a few concerns remain.
[1] -Of most substantial concern is the timeline of the data collected.Specifically, as the authors highlight, the collected data is from 1994-1995.While the results and discussion presented are interesting, it is difficult to determine whether similar results would be found in today's adolescent population.With the social landscape of 1994-1995 being quite different from today (e.g., prevalence of social media, online friendships, etc.), it would helpful for the authors to discuss how their findings may be translated to be relevant for adolescents in 2023.Similarly, the average age of pubertal onset is younger today than 20-30 years ago-how might an even earlier pubertal onset for some further influence friendship formation and social connections?(1) H1: One plausible hypothesis related to physical behaviors (PA, Sleep) is that that a greater extent of connection would amplify the magnitude of associations we see in terms of similarity of friends having similar physical behaviors.(2) H2: A competing hypothesis might be that perhaps social connection is in some ways "thinner" due to, arguably, less (and perhaps less meaningful) in-person interactions, making youth less likely to gravitate to those with similar behaviors, leading to a lower extent of friendship.[59] and has continued to decline, albeit more slowly, during the past several decades [60,61]."In terms of theorizing how earlier pubertal onset might influence friendship formation and social connections, we might hypothesize several scenarios.

• (b) Secular changes in puberty timing: As to the declining age of puberty, we have now added an explicit statement first acknowledging this point on p14, "In terms of pubertal development, the onset of puberty rapidly declined since the industrial revolution
(1) H1: uniform decline in pubertal timing does not lead to appreciable change in puberty similarity among friends due to uniform decline in pubertal timing: in one scenario, due to consistent declining onset across youth, similarity in pubertal timing among connected friends does not change meaningfully.
(2) H2: uniform decline in pubertal timing leads to more friendship turnover.Here we take inspiration from scholars of adolescent development [59,80], who point out that looking at secular changes in pubertal development are not likely to be as productive as investigating the growing gap between one's age of physical maturity (going down) and age of psychosocial maturity (going up).This widening gap might lead to an increase in risk-taking health behaviors and possibly riskier friendships made without thought or care, leading to more turnover, fewer solid connections, fewer "best friendships" and so forth.In some ways, the socialization loss currently being observed among youth who spent some part of 2020-2021 with impaired learning due to COVID-19 might give us leverage on the question of what might happen if ability to form social connections was inhibited/disrupted.Interestingly, we can see this uncertainty leading to less similarity on pubertal timing among friends, but inconsistency and uncertainty in socialization might prompt a kind of social development recession wherein youth would seek friends with some type of trait similarity, pubertal timing status included.
(3) H3: uniform decline in pubertal timing leads to less friendship turnover/more stability.Although it is possible, this scenario seems unlikely due to the widening gap between physical and psychosocial maturity mentioned in H2.
(4) H4: Non-uniform decline in pubertal timing leads to differential effects for subpopulations.If changes in onset of puberty and pubertal tempo are happening at different rates for girls and boys, and/or racial/ethnic groups, for instance, we might also hypothesize differential effects for subpopulations.
Reviewer #4: This is a well-written manuscript.I liked reading this manuscript and believe that it is very promising.At the same time, I identified couple of issues that require the authors' attention.Introduction is too long and same goes with the conclusion and discussion which can be combined and shortened to improve the readability of the article.Professional use of English language is at par.Overall, this will be a good addition to current available literature.

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We thank R3 for their concerns about the time at which the data were collected, a concern shared by R1, and by our team as well.Carefully reconsidering the possibilities has led to insights that we think enhance the paper appreciably.It is indeed an interesting question whether similar results would be found among today's youth, and ultimately, we argue that (a) our associational findings are likely to be conservative relative to today's youth, and (b) we hope that one contribution of this study is to provide a roadmap for one way to study the associations (and hopefully, prospective associations in a longitudinal framework) between physical development and friendships (p25-26).It bears noting that interpersonal mechanisms like social comparison, social desirability, and popularity existed then, and still drive a great deal of adolescent (to say nothing of adult!) behavior.We look forward to our colleagues in the field continuing to build datasets that would allow us to confirm this assumption; we now point out useful possibilities of extending existing data sources, and offer strong advocacy for this type of research with new text on p25 (line 23)-p26 (lines 1-3).To our minds, there are intersecting issues here: changes in screen use, and changes in puberty timing which may have independent and interactive effects on friendship formation and maintenance.By themselves, each issue provokes several competing hypotheses.Taken together, it is difficult to predict specific outcomes, though we use the below thinking outlined below to more clearly point to this uncertainty and highlight some possibilities on p24-25 to help readers bridge between findings from data gathered several decades ago with the current moment.Though this kind of speculation is useful to provoke new hypotheses to test as extensions of this research, it is currently beyond the scope of this already somewhat lengthy paper to include the below hypothesizing in its entirety.•(a) Secular changes in screen use: It is certainly plausible that today's youth are more densely connected to one another due to ubiquitous screens and online presence, though some might argue that at least some of this social connection is relatively insubstantial.Social network scholars have recently called for more attention to theorizing the causes and consequences of offline versus online friendships[56], a point we now reinforce on page 24.

(Knox & TenEyck 2023; Jose et al. 2021; Verweij & Keizer 2022), similar to open-access policies in other publications such as Nature, Nature Human Behaviour, Nature Communications, PNAS, and Scientific Reports (we can provide a more comprehensive citation list if editors require it). References: Knox, Krysta N. & TenEyck, Michael F. (2023). Beauty is only skin deep: An examination of physical attractiveness, attractive personality, and personal grooming on criminal justice outcomes. PLOS ONE. vol. 18 (10), PMCID: PMC10566695 Jose, R.; Hipp, J. R.; Butts, C. T.; Wang, C.; & Lakon, C. M. (2021). A multi-contextual examination of non- school friendships and their impact on adolescent deviance and alcohol use. PLoS One. vol. 16 (2) , PMCID: PMC7875427 Verweij, R. M. & Keizer, R. (2022). The intergenerational transmission of educational attainment: A closer look at the (interrelated) roles of paternal involvement and genetic inheritance. PLoS ONE. vol. 17 (12 December) , PMCID: PMC9744317
4. Please include captions for your Supporting Information files at the end of your manuscript, and update any in-text citations to match accordingly.Please see our Supporting Information guidelines for more information: http://journals.plos.org/plosone/s/supporting-information.Authors: Thank you.

We have now appended a new subhead and caption for our Supporting Information file at the end of the manuscript (page 28, lines 2-4).
. Please review your reference list to ensure that it is complete and correct.If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references.Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript.If you need to cite a retracted article, indicate the article's retracted status in the References list and also include a citation and full reference for the retraction notice.

Authors: Thank you for this question. We have now updated p7 to include more detail about how pubertal timing affected sleep activity in Hoyt et al. (2020). The revised text now reads, "However, there was also some evidence that later timing is associated with health promoting
2. Could the authors please explain how pubertal timing affected sleep activity in the Hoyt et al study, 2020.

The revised text now reads,"Although we are limited in what we can infer from the self-reported measures of puberty (e.g. Add Health does not include physician-administered Tanner staging or hormone samples) and we have no information on pubertal tempo (which requires repeated puberty assessment starting in childhood), the pubertal development measures have adequate variation, and these measures have been examined in high-quality analyses exploring pubertal development [20, 27, 54]" 6
. The discussion may further expand on the utility of these findings in a greater way.Authors

: Thank you for this comment -in conjunction with comments by R2, R3, and R4, we have significantly expanded on the conclusions to draw the links to practical take-aways for readers and to contextualize why findings from a study conducted with 1994-95-era youth is still relevant today. 7
. The authors may want to add a limitations section to ennumerate the limitations related to the date of the data collection and possibly add what steps may be taken to possibly replicate the study in todays pubertal adolescents in order to have some more impactful results that have further value.Authors